It has been known for quite some time to use retractable balls mounted on a spring.
In this regard, mention may be made, for example, of the device described in the French patent application published under the number FR 2 600 869. This device is intended in particular for the closing and the locking of a bracelet. It comprises (cf. FIG. 1 of FR 2 600 869) a U-shaped member 1 comprising, at each end of the branches 4 and 4′ of the U, a lug 6 or 6′ at the end of which is situated a ball 15 mounted on a spring, which ball is intended to snap-fasten into a receiving cavity 16 formed in a receiving member 2 cooperating with the U-shaped member 1, in order to form a connection between the members 1 and 2.
In this device, an upper pivoting flap 12 can be swiveled down to entrap the lugs 6 and 6′ and thus lock the connection between the two members 1 and 2 (cf. FIG. 3 of FR 2 600 869). The upper pivoting flap 12, also called a safety lock, particularly has the function of blocking the lugs 6 and 6′ in their housing and of thus opposing an accidental disengagement.
However, if the end 3 is pulled in a direction perpendicular to the plane in which the opposite end 3′ is situated, that is to say upward, the safety lock 12 opens and no longer opposes the disengagement of the lugs 6 and 6′. Moreover, the force of the positioning springs is not sufficient to retain the two balls in their housing 10, 10′. Furthermore, the free end (not numbered) of the safety lock 12, which comes to be housed behind the articulation 8 (cf. FIGS. 5 to 7 of FR 2 600 869) is worn and/or buckled too quickly. The safety lock 12 then pivots too easily and can no longer fulfill its function of preventing an accidental disengagement of the lugs 6 and 6′ from their respective receiving housings 10 and 10′.
Also known are clasps such as that described in International Application No. WO96/31138. The main disadvantages of such a clasp are the following:                it is very difficult to assemble,        it comprises a large number of parts, in particular four springs,        the upper part of its locking stud wears with time,        the inner walls of its safety cover end up by being marked with grooves due to the friction of the ends of the locking elements, and        the safety cover must, in its first embodiment, allow a certain degree of elastic deformation to allow the clasp to close.        
Moreover, Swiss Patent No. 624 836 describes a bracelet clasp comprising a ball tube comprising a ball at each end and a spring intended to exert an outwardly directed force on the balls.
On the other hand, the subject of Swiss Patent No. 207 554 is a device for attaching a watch bracelet link provided with a tube having, at each of its ends, a stop in contact with a helical spring.